This invention relates to rotating electrical machines in which the rotor comprise a permanent magnet, and more particularly to those motors in which the rotor is supported by a spherical bearing engaged into an axial cavity of the rotor.
In an electrical machine wherein the rotor comprises a permanent magnet and a bearing cap pivotally supported by a magnetized rotor is a stationary bearing ball mounted on the tip of a pillar or post that is engaged into a cylindrical axial channel of the rotor, the bearing cap has a hole at its apex so that part of the pump fluid can leak through it to lubricate the bearing surfaces. The portion of the cap which is in contact with the ball, thus, defines a truncated hemispherical or frusto-spherical zone having at its top, the small diameter of the hole and at its base, a diameter closely matching the diameter of the ball so that small radially-directed forces can be absorbed. In prior art spherical motors where the permanent magnetic forces are generated by the stator winding, the magnetic lines of force run substantially parallel to each other across the air gap between the magnetic poles of the stator. These lines remain parallel even when the rotor moves eccentrically. The parallel magnetic forces have no tendency to increase the eccentric deviation of the rotor. However, in motors in which the rotor is formed by a strong permanent magnet, the magnetic lines of force across the air gap between the rotor and the stator follow divergent paths. If the rotor has a slight eccentricity, the magnetic pole which as moved closer to the stator is subject to increased magnetic forces while the opposite pole experiences a decrease in magnetic pull. This unbalance of forces exacerbates the deviation and tends to break the even and balanced contact between the bearing cap frusto-spherical zone and the ball. The axis of the bearing cap no longer matches that of the ball. The cap also tends to move axially away from the cap. A similar instability occurs in machines of the prior art every time the roto moves in such an axial way as may be caused, for instance, by a shock or other rapid acceleration.
This invention results from attempts to correct the aforesaid instability in machines with permanent magnet rotors.
The principal and secondary objects of this invention are to provide a rotor bearing configuration, in motors using a strongly magnetized rotor, that can withstand an even correct uniform bearing frictions due to slightly radially eccentric and axial movements of the rotor.
These and other valuable objects are achieved by providing a bearing surface for a single-ball bearing, or any other bearing structure having a hemispherical surface, that defines a cylindrical portion capped by a frusto-spherical sector whose radius is equal to the ball radius plus a desired clearance. An apical aperture having a radius of equal to approximately 60% of the ball radius allow lubricating fluid to reach the bearing surface.